The present invention relates to an image receiving layer of an image receiver for thermal transfer recording used for recording in which a high-temperature heating means for short time, for example a thermal head, an optical head such as a laser or an electrode head etc. is used, relates to an image receiver having an image receiving layer for thermal transfer recording, and relates to a thermal transfer recording method in which the image receiver is used. In particular, the present invention relates to an image receiving layer of an image receiver for thermal transfer recording of a sublimation dye transfer type, a melt dye transfer type, and the like, to an image receiver for thermal transfer recording having such image receiving layer, and to a thermal transfer recording method in which such image receiver is used.
A thermal transfer recording method is compact and excellent in maintainability and reliability, and furthermore is excellent in less electricity, high speed, prevention against tampering, color recording, and recording on plain paper, etc. Such thermal transfer recording method has received much attention as electronization of OA appliances have developed. An ink sheet for the thermal transfer recording method and an image receiver for the thermal transfer recording method (henceforth, referred to as a xe2x80x9cthermal transfer recording image receiverxe2x80x9d) are used in such thermal transfer recording method. The ink sheet generally comprises a substrate made of a plastic film or the like, a dye layer containing a thermally transferable dye on a front surface of the substrate and a heat-resistant sliding layer on a back surface of the substrate which provides a readily travelling property for a heating means. The thermal transfer recording image receiver generally comprises a substrate made of a plastic film or the like, and an image receiving layer placed on a surface of the substrate which receives the dye from the ink sheet. After arranging the thermal transfer recording image receiver on the ink sheet so that it overlaps the dye layer on the front surface of the ink sheet, the heat-resistant sliding layer of the ink sheet is heated with heat energy corresponding to an image information to be recorded by using the heating means, for example a thermal head, an optical head such as a laser, and an electrode head etc. By this heating, the thermally transferable dye contained in the dye layer of the ink sheet is transferred to the image receiving layer of the thermal transfer recording image receiver through its diffusion, so that the thermal transfer recording is carried out.
Among the thermal transfer recording methods, a melt dye transfer type or a sublimation dye transfer type thermal transfer recording method is particularly receiving much attention since quality of an image which is obtained by using such method has been improved beyond the quality of an image of the silver halide conventional photograph. The ink sheet is used in this method which has an ink layer containing a melt type transferable dye or subliming thermally transferable dye as the dye layer on the substrate. Recording is carried out by heating the dye layer with a heating means such as a thermal head to transfer (thermally transfer) the thermally transferable dye, through its thermal diffusion, to the image receiving layer of the thermal transfer recording image receiver which layer is in contact with the dye layer. (Hereinafter, merely xe2x80x9cto transferxe2x80x9d means xe2x80x9cto move a thermally transferable dye to an image receiving layer by transferring the dye through thermal diffusionxe2x80x9d.) Color recording is performed by thermally transferring, in sequence, a cyan (C) dye, a magenta (M) dye and a yellow (Y) dye contained into the ink layer to the image receiving layer by using the thermal recording head. An amount of the thermally transferable dye to be transferred can be controlled by varying the heat energy to be applied to the dye layer. Therefore, the melt dye transfer type or sublimation dye transfer type thermal transfer recording method is particularly preferable for full-color recording since a gradient recording can easily be carried out.
However, the thermal transfer recording method of the melt dye transfer type or sublimation dye transfer type has a problem in that it produces an image which is inferior to that of the silver halide conventional photography, for example, in an image grade (quality) such as glossiness and sharpness (clearness) of the image, and in an image shelf life such as heat resistance of the image. Moreover, there is a problem in that such thermal transfer recording method requires a higher running cost in comparison with the silver halide conventional photography. These problems would be caused by the thermal transfer recording image receiver rather than the ink sheet. In particular, the image receiving layer of the thermal transfer recording image receiver would relate to the image grade and the image shelf life, etc.
Japanese Patent Kokai Publication No. 60-25793 discloses an image receiving layer for such a thermal transfer recording image receiver. In this image receiving layer, since a plurality of resins which constitute the image receiving layer are incompatible with each other as shown in FIG. 8, the image receiving layer 3 becomes heterogeneous, and the plurality of the resins is phase-separated from each other. In FIG. 8, the image receiving layer 3 is formed on a surface of a substrate 2 of the thermal transfer recording image receiver 1 and the image receiving layer 3 is constituted of two kinds of incompatible regions 31 and 32. As the image receiving layer having such constitution, an image receiving layer is disclosed wherein a resin constituting the image receiving layer is composed of at least two kinds of thermoplastic resins, one of which has a glass transition temperature (Tg) of not higher than 20xc2x0 C., the other of which has a Tg of not lower than 40xc2x0 C., and regions of these two kinds of thermoplastic resins having the different Tg""s are present together. The thermally transferable dye which is originated from the dye layer of the ink sheet while corresponding to applied thermal recording signals passes mainly through the region of the resin having the lower Tg or interfaces between the regions of the two kinds of the resins to diffuse into the image receiving layer, so that the image is recorded in the image receiving layer.
Since the conventional image receiving layer as described above is lacking in the glossiness and the heat resistance etc., the glossiness and sharpness etc., of the image to be obtained are deteriorated, and it is difficult to obtain an image having a high grade. Moreover, since there is the region of the resin having the lower Tg, it is difficult to obtain an image having a good image shelf life such as a satisfactory heat resistance. Furthermore, since the two kinds of the resins are incompatible, a material to be applied from which the image receiving layer is formed is likely to be subjected to phase separation, and it is difficult to efficiently form the image receiving layer with desired phase separation. This contributes to the cost increase when the thermal transfer recording method is used.
Further, Japanese Patent Kokai Publication No. 61-283595 discloses a saturated polyester and a vinyl chloride-vinyl acetate copolymer as the resins to be used for such image receiving layer, and an amount of moieties derived from vinyl chloride in the vinyl chloride-vinyl acetate copolymer (which corresponds to a percentage of vinyl chloride in monomers when the vinyl chloride-vinyl acetate copolymer is obtained by polymerizing a monomer mixture) is from 85 to 97% by weight in the copolymer. Japanese Patent Kokai Publication No. 61-199997 discloses that a polyester resin, an isocyanate compound, and a silicone compound being capable of reacting with an isocyanate group are used for the image receiving layer. However, when the resin disclosed in the former document is used, there arise problems concerning heat resistance and stability of the image upon high-speed recording. The resin disclosed in the latter document has problems concerning an image grade such as glossiness and sharpness.
The present invention has completed in order to solve those problems. An object of the present invention is to provide a novel image receiving layer which alleviates or substantially solves at least one of the problems that an image grade (quality) such as glossiness and sharpness etc., of the image to be formed is deteriorated, an image shelf life such as heat resistance of the image is poor, and a running cost is high when the thermal transfer recording method is carried out. Moreover, an object of the present invention is to provide a thermal transfer recording image receiver having such image receiving layer, and also to provide a thermal transfer recording method in which such image receiver is used. In particular, an object of the present invention is to provide an image receiving layer to be used for a sublimation dye transfer type or melt dye transfer type thermal transfer recording, a thermal transfer recording image receiver having such image receiving layer, and a thermal transfer recording method in which such image receiver is used.
In an aspect of the present invention, a novel image receiving layer for the thermal transfer recording image receiver is provided, which layer is an image receiving layer (B) to be used for the thermal transfer recording image receiver comprising a sheet substrate (A) and the image receiving layer (B) placed on one of main surfaces of the substrate, and which layer is characterized in that it is formed from a composition comprising an acrylic polyol resin and the other thermoplastic resin. In another aspect of the present invention, a thermal transfer recording image receiver is provided in which such image receiving layer is used. In a further aspect of the present invention, a thermal transfer recording method is provided which uses such image receiver. Since the image receiving layer is formed from the composition comprising the acrylic polyol resin and the other thermoplastic, the image receiving layer of which strength and dye receiving property, and/or sharpness and so on of an image to be formed are improved can be provided.